sandbox: Improve sandbox serial port keyboard interface
Implements the tstc() interface for the serial driver. Multiplexing
the console between the serial port and a keyboard uses a polling
method of checking if characters are available; this means that the
serial console must be non-blocking when attempting to read
characters.
Signed-off-by: Taylor Hutt <thutt@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/sandbox.c b/drivers/serial/sandbox.c
index cb19401..b73520c 100644
--- a/drivers/serial/sandbox.c
+++ b/drivers/serial/sandbox.c
@@ -30,6 +30,19 @@
#include <serial.h>
#include <linux/compiler.h>
+/*
+ *
+ * serial_buf: A buffer that holds keyboard characters for the
+ * Sandbox U-boot.
+ *
+ * invariants:
+ * serial_buf_write == serial_buf_read -> empty buffer
+ * (serial_buf_write + 1) % 16 == serial_buf_read -> full buffer
+ */
+static char serial_buf[16];
+static unsigned int serial_buf_write;
+static unsigned int serial_buf_read;
+
static int sandbox_serial_init(void)
{
os_tty_raw(0);
@@ -50,18 +63,37 @@
os_write(1, str, strlen(str));
}
-static int sandbox_serial_getc(void)
+static unsigned int increment_buffer_index(unsigned int index)
+{
+ return (index + 1) % ARRAY_SIZE(serial_buf);
+}
+
+static int sandbox_serial_tstc(void)
{
- char buf;
+ const unsigned int next_index =
+ increment_buffer_index(serial_buf_write);
ssize_t count;
- count = os_read(0, &buf, 1);
- return count == 1 ? buf : 0;
+ os_usleep(100);
+ if (next_index == serial_buf_read)
+ return 1; /* buffer full */
+
+ count = os_read_no_block(0, &serial_buf[serial_buf_write], 1);
+ if (count == 1)
+ serial_buf_write = next_index;
+ return serial_buf_write != serial_buf_read;
}
-static int sandbox_serial_tstc(void)
+static int sandbox_serial_getc(void)
{
- return 0;
+ int result;
+
+ while (!sandbox_serial_tstc())
+ ; /* buffer empty */
+
+ result = serial_buf[serial_buf_read];
+ serial_buf_read = increment_buffer_index(serial_buf_read);
+ return result;
}
static struct serial_device sandbox_serial_drv = {